The only tricks I find disrupted by a weight imbalanced setup are spacewalk / air-tricks, and probably juggles. Otherwise, if tama is 0-9% heavier or so, it's fine by me (that works out to about 7-8 grams for your average ken). I bought a keyaki Sanga at KWC that is like 20 grams off (tama heavy). Sucks to spacewalk but cup game is great on it.
I am surprised to hear that a retailer was trying to be dishonest, that is never a good experience. I appreciate it is hard to offer accurate weight matching on competitively priced kendamas though. Terra sometimes offers guarantees such as 'within 5 grams', but in reality they were all within 2.5 grams on my scale, just to be safe. Wood is a variable material, and it can pick up (or lose) weight through moisture, so when a customer receives the product, it can be different on their scale. On small scale Terra productions we will list the weight of each individual piece, but doing this at scale for lower priced items would be a nightmare!